The most recent thread I can find on this issue is from 2013. As with many other topics, the parts and services available for these vehicles have changed dramatically in the last 11 years, as has the potential value of these trucks and their use in the future (most IDIs still on the road, especially restoration projects like mine, aren’t going to be regularly used as work trucks).
(Also, I am not a new member but it’s been years since I’ve posted and have since gotten a new email.)
Long story short, I recently picked up an ‘84 3/4-ton 6.9 4-speed. 150k, cab was in excellent condition. Seller was not great in responding to questions or sending pictures but the price was right (I already had a decent Bullnose parts truck with a 302 and a good bed) so I hooked up the trailer and drove 5 hours to pick it up.
Knowing that early blocks had the potential to crack, but not having any firsthand experience with the IDI, I made sure it didn’t have any fuel or coolant leaks but did not check to see if the engine had been replaced, engine serial number, etc, nor did I look for an actual crack. A few days after getting it home, I noticed a puddle of coolant on the floor of my shop.
Here’s what I found:
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At first I thought the leak might be from a bad o-ring in the block heater, but after cleaning the area up I could visibly see coolant seeping through what looks to me like a crack. I’m wondering if the PO used radiator stop leak or something like that to plug the leak or if the stress tests I put on it when I first brought it home caused the crack to expand.
The engine serial number is 6.9DU2U081650F, putting it well below the cutoff between the new style and old style blocks. This is the truck’s original engine and as far as I can tell it has never been removed from the truck for an overhaul.
Other than this fun surprise, the engine runs great. Virtually no blowby, a bit on the smoky side but barely noticeable when warm. The engine is significantly louder than I expected, with significantly more valvetrain noise than my Perkins and Mercedes diesels of the same vintage (for more of an apples-to-apples comparison, it has far more valvetrain noise than I remember my 7.3 PSD having).
Other than the engine, IMO the truck is a great restoration candidate; it’s worn but the biggest deferred maintenance items will be rebuilding the front end and putting new seals on the transfer case and rear axle.
So the question is: what’s the solution? As a restoration project, not as just an old truck that could be easily replaced for a couple grand, what are my options in 2024? (Personally, I haven’t rebuilt an engine since shop class 20 years ago and I’m pretty sure that one didn’t run. Ideally, I’d remove the engine mostly complete, take it or ship it to a shop, and have it returned mostly complete.)
My preference would be to keep the truck as original as possible, and the cost of buying a crate engine would be prohibitive (especially considering I don’t believe they’d take my engine as a core). I had a head crack on a tractor a few years ago and the shop I took it to was able to send it out for some type of coating process (I can’t think of the name), would a tig weld and something like that be a lasting repair? If I was able to find a later 6.9 block am I going to run into issues with warping or compatibility (such as with the 7.3 IDI, which has larger head studs)?
(Also, I am not a new member but it’s been years since I’ve posted and have since gotten a new email.)
Long story short, I recently picked up an ‘84 3/4-ton 6.9 4-speed. 150k, cab was in excellent condition. Seller was not great in responding to questions or sending pictures but the price was right (I already had a decent Bullnose parts truck with a 302 and a good bed) so I hooked up the trailer and drove 5 hours to pick it up.
Knowing that early blocks had the potential to crack, but not having any firsthand experience with the IDI, I made sure it didn’t have any fuel or coolant leaks but did not check to see if the engine had been replaced, engine serial number, etc, nor did I look for an actual crack. A few days after getting it home, I noticed a puddle of coolant on the floor of my shop.
Here’s what I found:
At first I thought the leak might be from a bad o-ring in the block heater, but after cleaning the area up I could visibly see coolant seeping through what looks to me like a crack. I’m wondering if the PO used radiator stop leak or something like that to plug the leak or if the stress tests I put on it when I first brought it home caused the crack to expand.
The engine serial number is 6.9DU2U081650F, putting it well below the cutoff between the new style and old style blocks. This is the truck’s original engine and as far as I can tell it has never been removed from the truck for an overhaul.
Other than this fun surprise, the engine runs great. Virtually no blowby, a bit on the smoky side but barely noticeable when warm. The engine is significantly louder than I expected, with significantly more valvetrain noise than my Perkins and Mercedes diesels of the same vintage (for more of an apples-to-apples comparison, it has far more valvetrain noise than I remember my 7.3 PSD having).
Other than the engine, IMO the truck is a great restoration candidate; it’s worn but the biggest deferred maintenance items will be rebuilding the front end and putting new seals on the transfer case and rear axle.
So the question is: what’s the solution? As a restoration project, not as just an old truck that could be easily replaced for a couple grand, what are my options in 2024? (Personally, I haven’t rebuilt an engine since shop class 20 years ago and I’m pretty sure that one didn’t run. Ideally, I’d remove the engine mostly complete, take it or ship it to a shop, and have it returned mostly complete.)
My preference would be to keep the truck as original as possible, and the cost of buying a crate engine would be prohibitive (especially considering I don’t believe they’d take my engine as a core). I had a head crack on a tractor a few years ago and the shop I took it to was able to send it out for some type of coating process (I can’t think of the name), would a tig weld and something like that be a lasting repair? If I was able to find a later 6.9 block am I going to run into issues with warping or compatibility (such as with the 7.3 IDI, which has larger head studs)?
